Manganite composition



Patented May 4, 1954 UNITED STATES 2,677,663 TENT OFFICE MANGANETECOMPUSITION No Drawing. Application February 4, 1950, Serial No. 142,525

@Iaims priority, application Netherlands February 5, 1%9

11 Claims.

This invention relates to magnet cores and particularly to coresconstituted by manganites.

A manganite is an oxygen compound of manganese and a second bivalent ortrivalent metal. More particularly, manganites as referred tohereinafter in the specification and in the claims are compositionswhich have the general formulae lM Mnos and M D/Z1103 According to theinvention, the magnet cores are constituted by essentially homogeneousmixed crystals of two or more of the foregoing manganites. The termmixed crystal refers to the crystalline combination or two or more suchmanganites which are solid solutions of the manganites having a commonchemical character istic. More specifically, the mixed crystal is a newchemical compound of the individual manganite having a substantiallyhomogeneous crystalline structure.

The mixed crystals are preferably composed in a stoichiometric ratio oftwo or more manganites but it is not essential that they be in exactstoichiometric ratio, and the mixed crystals may contain a slight excessor deficiency of oxygen a slight excess or deficiency of manganese, andstill be satisfactory for the purposes or" the invention.

The mixed crystals of the manganites may also contain additionalcompounds such as ferrites, c romites, titanates and aluminates, withoutdeting from the inventive concept.

The mixed crystals of the manganites do not all have a purely cubiccrystalline structure since ratios of the axes and the axial angles ofcrystal system may slightly depart from se of the cubic crystal, system.

In describing the invention, particular referenoe will be made tolanthanum manganite. owever, the invention is not restricted solely totoe case where lanthanum manganite is one of the constituents of themixed crystal. The purof describing the invention in connection withlanthanum manganite is that the perowskits structure of the mixedcrystal requires a large ion at the position of the M in the crystallattice which is furnished most conveniently by the lanthanum ion.

this connection it is to be noted that there other manganites which mayhave no perow- 2 praseodymium manganite and neodymium manganite.

Other manganites which are suitable for the purpose of the invention andwhich will be described more completely in the examples to be givenlater, are manganites of strontium, barium and lead, and in connectionwith desired mag netic properties to a lesser degree, those of calciumand cadmium, even though not all of these materials, taken individually,exhibit a perowskite structure.

However, in determining the formation of crystals having a perowskitestructure, there is a definite limit for the replacement of thelanthanum in lanthanum manganite. For example, the lanthanum inlanthanum manganite may be replaced by strontium to the extent ofapproximately at most, and at most by 50% by barium or lead. Exceedingthe limit set for the substitution by other constituents results in acrystal phase different than the perowskite phase.

Partially substituting another manganite for lanthanum manganite has theeiiect of varying the curie point of the mixed crystal manganite, thecurie point being that temperature at which, for all practical purposes,the material exhibits no ferromagnetic properties, i. e., it isparamagnetic By replacing some of the lanthanum manie in the mixedcrystal with strontium, barium and/or lead manganite, a curie pointexceeding room temperature can be readily ob- Mixed crystals including25 to 50 mol. per cent of strontium, barium, or lead manganite,

" respectively, and containing '75 to 49 mol. per cent of lanthanummanganite, has a curie point between 6:? and 99 C., which is abovenormal ambient temperatures, in which event these materials are suitablefor magnet cores.

In this connection it is to be noted that various mixed crystals ofmanganites exhibit a curie point which is below 0 C. and consequentlysuch materials have no ferromagnetic properties at normal ambienttemperatures. A comparatively pure lanthanum manganite containing 4% ofmanganese which is tetravalent, has a curie point below -200 C. If theperowskite structure is retained and no second phase exists in thematerial, the said material may contain more than 25% manganese intetravalent form, so that a material of the formula LaMnO3 1e5 may, fore 'nple, be obtained having a curie point in the neighbourhood of 20 C.By partly replacing the lanthanum in the lanthanum manganite by one ofthe bivalent metals, the curie point can be raised to a temperatureabove 0 C. If the lanthanum is replaced by strontium, barium and/orlead, it is possible to obtain material at ambient temperatures havingan initial permeability of 106 to 200 which was measured at 4 ire/sec.and a magnetic saturation of approximately 60 gauss cm. /g.

Substitution of Al, Cr, Ti, Fe, Co or Ni, for example, for part of theMn, generally involves a lower curie temperature. For this reason only alimited substitution of these metals is desirable.

The mixed crystals of the manganites may be prepared by reaction of amixture of the constituent metal oxides or compounds which decomposeinto these oxides upon heating, or compounds which in addition to one ormore of the desired metal oxides contain only volatile components. Theconstitution of this mixture, the reaction temperature, the partialoxygen pressure of the ambient atmosphere at the reaction temperature,and the partial oxygen pressure of the cooling atmosphere all determinethe oxygen content of the mixed crystal thus formed.

The magnet cores according to the invention are produced by conventionaltechniques employed in the ceramic industry, the material being used inthe form of powder during the sintering and cooling operations and theconditions being such as to prevent conversions adversely aiiecting themagnetic properties, such as the formation of undesirable second phasesin the material. After shaping the initial mixture, the preparation ofthe desired mixed crystals and the sintering operation required for themanufacture of the magnet cores may alternatively be effected in oneoperation. Finally, the mixed crystals in question may be fabricatedinto magnet cores with the use of a binder.

The invention will be described in connection with the followingexamples which indicate several preferred embodiments of the invention.

EXAMPLE I A mixture of 130 gms. of lanthanum carbonate, 29.5 gins. ofstrontium carbonate and 115 gms. of manganese carbonate is sintered inair at 900 to 1000 C. for several hours. After cooling, the mixture isground and molded into the desired shape, followed by sintering in airat a temperature between 1370 and 1 150 C. for three hours. The magnetcore obtained consists of essentially homogeneous mixed crystals of 80mol. percent lanthanum manganite and mol. percent strontium manganite.In a similar manner, mixed crystals of 70 mol. percent lanthanummanganite and mol. percent strontium manganite, of 60 mol. percentlanthanum manganite and mol. percent strontium manganite and of mol.percent lanthanum manganite and 50 mol. percent strontium manganite areproduced. If the composition contains more than 40 mol. percent of MMnOs, it is desirable to use an atmosphere having a higher partialpressure of the oxygen or even pure oxygen. Several magnetic propertiesare stated in the following table.

A mixture of 130 gms. lanthanum oxide, 39.5 barium carbonate and 115gms. manganese carbonate is sintered in air at 900 to 1000 C. forseveral hours. After cooling, the mixture is ground and moulded into thedesired shape, followed by sintering in air at a temperature between1370 and 1450" C. for three hours, thus obtaining a magnet coreconsisting of essentially homogeneous mixed crystals of mol. percentlanthanum maganite and 20 mol. percent barium manganite. In a similarmanner, mixed crystals of 75 mol. percent lanthanum manganite and 25mol. percent barium manganite, of 70 mol. percent lanthanum manganiteand 30 mol. percent barium manganite and of 65 mol. percent lanthanummanganite and 35 mol. percent barium manganite are formed. Severalproperties are stated in the following table.

ccuww macro EXAMPLE III A mixture of 160 gms. lanthanum carbonate, 14.3gms. strontium carbonate, 103.5 gms. manganese carbonate and 5.1 gms.aluminium oxide is sintered in air at 900 to 1000 C. for several hours.After cooling, the mixture is ground and moulded into the desired shape,followed by sintering in air at a temperature between 1370 and 1450" C.for three hours. The magnet core obtained. may be conceived to consistof essentially homogeneous mixed crystals of 60 mol. percent lanthanummanganite, 10 mol. percent lanthanum aluminate (LaAlOs) and 30 mol.percent strontium manganite. The curie-temperature is 43 C. and themagnetic saturation l7 gauss. cm. /g. at 20 C.

EXAMPLE IV A mixture of 114 gms. lanthanum oxide, 4 1.3 gms. strontiumcarbonate, 32.6 gms. manganese eroxide and 4 gms. of ferrioxide issintered in air at 900 to 1000 C. for several hours. After cooling, themixture is ground and moulded into the desired shape, followed bysintering in air at a temperature between 1370 and 1450" C. for threehours. The magnet core obtained may be conceived to consist ofessentially homogeneous mixed crystals of 65 mol. percent lanthanummanganite, 5 mol. percent lanthanum ferrite and 30 mol. percentstrontium manganite. The curie-temperature is 70 C. and the magneticsaturation 39 gauss. cm. /g. at 20 C.

EXAMPLE V A mixture of 114 gms. lanthanum oxide, 22.1 gms. of strontiumcarbonate, 29.6 gms. of barium carbonate and 115 gms. manganesecarbonate is sintered in air at 900 to 1000 C. for several hours. Aftercooling, the mixture is ground and moulded into the desired shape,followed by sintering in air for three hours at a temperature between1370 and 1450 C. The magnetic core obtained consists of essentiallyhomogeneous mixed crystals of 70 mol. percent lanthanum manganite, 15mol. percent strontium manganite and 15 mol. percent barium manganite,the curie temperature being 70 C., and the magnetic saturation in gauss.cmfi/g. at 20 C. being 57. The initial permeability with 4 kc./sec. andat C. was found to be 180.

EXAMPLE VI A mixture of 114 gms. of lanthanum oxide, 80 gms. of leadcarbonate and 115 gms. of maganese carbonate is sintered in air forseveral hours at 900 to 1000 C. After cooling, the mixture is ground andmoulded into the desired shape, followed by sintering in air at atemperature gradually increasing from 1100 to 1300 C. for three hours.The magnet core obtained consists of essentially homogeneous mixedcrystals of 70 mol. percent lanthanum manganite and 30 mol. percent oflead manganite, the curie-temperature being 90 C. and the magneticsaturation in gauss. cm. /g. at 20 C. being 36.

While we have thus far described our invention with specific examplesand methods of preparation, other modifications thereof will be obviousto those skilled in the art without departing from the spirit and scopeof the invention.

What we claim is.

1. A new composition of matter consisting essentially of homogeneousmixed crystals of a manganite having the formula M+ MnO3, M++ being ametal selected from the group consisting of strontium, barium, and lead,and a manganite having the formula M+++Mn0s, M+++ being a metal selectedfrom the group consisting of lanthanum, praeseodymium and neodymium,said mixed crystals having a perowskite crystal structure.

2. A new composition of matter as claimed in claim 1 in which the mixedcrystals include a material selected from the group consisting of aferrite and an aluminate.

3. A new composition of matter as claimed in claim 1, in which the mixedcrystals contain approximately between to 50 mol. percent of amangani'te selected from the group consisting of strontium manganite,barium manganite and lead manganite, and approximately 75 to 50 mol.percent of lanthanum manganite.

4. A new composition of matter as claimed in claim 1, in which the mixedcrystals include a ferrite.

5. A new composition of matter as claimed in claim 1, in which the mixedcrystals include an aluminate.

6. A new composition of matter consisting of essentially homogeneousmixed crystals constituted by approximately between to 80 mol. percentof lanthanum manganite and approximately 20 to 40 mol. per cent ofstrontium manganite.

'7. A new composition of matter consisting of essentially homogeneousmixed crystals of approximately between and 80 mol. per cent oflanthanum manganite and approximately between 20 and 35 mol. per cent ofbarium manganite.

8. A new composition of matter consisting of essentially homogeneousmixed crystals of 60 mol. per cent of lanthanum manganite, approximately10 mol. per cent of lanthanum aluminate and approximately 30 mol. percent of strontium manganite.

9. A new composition of matter consisting of essentially homogeneousmixed crystals of approximately 65 mol. per cent of lanthanum manganite,approximately 5 mol. per cent of lanthanum ferrite and approximately 30mol. per cent of strontium manganite.

10. A new composition of matter consisting of essentially homogeneousmixed crystals of approximately mol. per cent of lanthanum manganite,approximately 15 mol. per cent of strontium manganite and approximately15 mol. per cent of barium manganite.

11. A new composition of matter consisting of essentially homogeneousmixed crystals of approximately 70 mol. per cent of lanthanum manganiteand approximately 30 mol. per cent of lead manganite.

References Cited in the file of this patent UNITED STATES PATENTS Number

10. A NEW COMPOSITON OF MATTER CONSISTING OF ESSENTIALLY HOMOGENEOUSMIXED CRYSTALS OF APPROXIMATELY 70 MOL. PER CENT OF LANTHANUM MANGANITE,APPROXIMATELY 15 MOL. PER CENT OF STRONTIUM MANGANITE AND APPROXIMATELY15 MOL. PER CENT OF BARIUM MANGANITE.